1. Field of the Invention
This invention relates generally to power systems and more particularly to uninterruptible power systems.
2. Description of the Related Art
A basic function of an uninterruptible power system (“UPS”) is to ensure continued delivery of power to loads (e.g., appliances, electronics, industrial equipment, etc.), even under a variety of primary power fault conditions and disturbances. A UPS may include, for example, a primary power source (e.g., an alternating current (AC) utility source delivered from a power grid) that provides power to loads, and a secondary power source (e.g., a battery or an AC generator) that can provide additional power to supplement the primary power source. Under “normal” operating conditions (e.g., when the primary power source is operating within defined, acceptable, operating limits of voltage and frequency), power for loads can be provided by the primary power source. Under “abnormal” operating conditions (e.g., when the primary power source is not operating within defined, acceptable, operating limits of voltage and frequency), the power for loads can be provided (at least partially) by the secondary power source. For example, in the event the primary power source fails, the secondary power source can be used to power to the loads.
Although alternative energy sources (e.g., solar power, wind power, hydro power, geothermal power, and the like) are increasing in use and popularity, they often contribute to degradation in the quality of the AC power provided by a power grid. Compared to conventional large-scale AC power generation facilities, alternative power sources are more likely to exhibit power interruptions and power quality issues, thereby contributing to a variety of power line disturbances (e.g., power sags, power surges, undervoltage or overvoltage conditions, transients associated with source switching on the utility line, utility line noise, frequency variations, harmonic distortion, line brownouts, line dropouts and the like). Unfortunately, contemporary loads (e.g., electronic loads) often require an uninterrupted flow of high quality AC power. For example, electronic components may require a supply of AC power that is within a given voltage and frequency ranges. Thus, it is desirable to provide a UPS that can reduce or eliminate the effects of line disturbances on the quality of the AC power it delivers.